Electrical characterization of metal/AlN/6H-SiC (0001) heterostructures

Metal/AlN/n-type 6H-SiC (0001) (MIS) heterostructures have been prepared by epitaxially growing wurtzite AlN layers on both vicinal and on-axis 6H-SiC (0001) substrates using gas-source molecular beam epitaxy. The capacitance-voltage characteristics obtained for these MIS heterostructures are found to depend strongly on temperature in the range from 200 to 573 K, and to exhibit hysteresis effects consistent with the presence of slow interface traps. The amount of hysteresis is found to increase with decreasing temperature. This can be explained in terms of the shift of the Fermi level closer to the semiconductor conduction band with decreasing temperature, causing the emission rate of the trapped charge to be less dependent on temperature. Cross-sectional high-resolution transmission electron microscopy results show that the interface formed on the vicinal 6H-SiC (0001) substrate contains a higher density of defects than that on the on-axis substrate. However, these two interfaces are found to have a similar density of trapped negative charge of 3×10¹¹ cm^-2 at room temperature, which decreases with increasing temperature. These results indicate that the interface between AlN and Si-terminated 6H-SiC (0001) is of a high quality suitable for device application